Gas turbine plant and method of operating the same



Nov. 12, 1963 5. FRANK ETAL I 3,110,473

GAS TURBINE PLANT AND METHOD OF OPERATING THE SAME Filed June 6, 1958 INVENTORS. BERTHOLD FRANK JOACHIM NITSCHKE BY w W 3,110,473 GAS TURBTNE PLANT AND METHGD F GPERATDJG THE SAME Berthold Frank and Joachim Nitschke, Ludwigshafen (Rhine), Germany, assignors to Badische Anilin- & Soda-Fahrik Alrtiengesellschaft, Ludwigshafen (Rhine), Germany Filed June 6, 1958, er. No. 740,485 Claims priority, application Germany June 7, 1957 1 Qlaim. ((Il. 25339.l5)

This invention relates to gas turbines with cooled rotors. It relates especially to the so-called evaporative cooling of a turbine rotor in which the cooling liquid evaporating in the rotor is moved in circulation.

In an evaporative cooling process, the turbine rotor automatically pumps the coolant from a container and sucks it into the hollow spaces in the rotor. The vapor can be withdrawn from the rotor at a pressure which is higher than the admission pressure of the coolant. If the 7 pressure of the cooling liquid entering the rotor is kept constant, the level of the liquid in the rotor can be maintained at the required height by controlling the vapor pressure in the rotor. The amount of liquid coolant introduced into the rotor is automatically the same as that which is vaporized therein. A device indicating the water level is not required in the rotor. With evaporative cooling the process is therefore simpler and safer to control.

It has become evident, however, that evaporative cooling is also attended by a series of difiiculties which in a continuous operation render its use difiicult and in some cases even prohibit its use.

In evaporative cooling, there is positively formed in the hollow spaces of the rotor of the gas turbine an interface between vapour and liquid. Oscillations occur at the liquid surface which cannot be prevented by insertions in the hollow spaces of the rotor. These oscillations often rise and become so strong that the turbine is to be brought to a standstill.

Furthermore, by the heating of the cooling liquid in the feed-in system of the turbine rotor, vapour bubbles form which interrupt the self-inductive supply of the liquid to the rotor. Additionally, the liquid level in the hollow spaces of the rotor is displaced somewhat outwards with increasing vapour pressure, for example by stronger evaporation of the liquid, or when the speed of rotation of the rotor decreases and the vapour pressure remains constant. Boiling liquid is thereby forced back into the liquid feed-in system of the rotor in which previously cold water was present. The hot water has a lower specific gravity. Therefore, still more hot water flows from the interior of the rotor until the rotor is completely emptied. The feeding of the liquid in a self-inductive manner is thus very unstable in this case.

It is an object of the present invention, therefore, to provide an apparatus and method which substantially eliminate the oscillations caused by instabilities at the interface between vaporous and liquid cooling medium.

Other objects will become apparent to those skilled in the art from the following detailed description of the invention.

We have now found that the above described disadvantages are avoided when the cooling liquid is supplied to the turbine rotor through a check-valve and when there is arranged parallel to the check-valve a pump which continually conveys a part of the liquid evaporating in the rotor. It is furthermore adavntageous to insulate the cooling liquid feed-in system of the rotor from heat transfer from the remaining parts of the rotor, especially the rotor blades, and to reduce the temperature of the cooling liquid to be supplied to the rotor to a value which lies considerably below the boiling point of the liquid.

Patented Nov. 12, 1%63 If the position of the interface between vapour and cooling liquid in the hollow spaces of the rotor is unstable, the check-valve prevents egress of the cooling liquid from the rotor. In this case the pump conveying a partial amount of the evaporating cooling liquid has only to apply a small increase in pressure until such an amount of cooling liquid has evaporated that equilibrium again prevails and the check-valve opens. Stable conditions exist when a partial amount of the liquid to be supplied to the rotor flows through the check-valve. Then no pressure increase takes place in the pump, it being merely necessary to ensure that the pump runs continuously. Otherwise, shortly after the check-valve shuts the cooling liquid stationary in the feed system will evaporate and the new coolant in the liquid state can only then be fed against an essential higher vapour pressure prevailing in the hollow spaces of the rotor. Then the stufiing boxes arranged at the place where the liquid is fed in would be strongly overloaded or damaged. By the arrangement according to this invention, the self induction of the rotor and the simple control of the coolant circulation thereby resulting is maintained in all cases and oscillations and instabilities of the evaporative cooling are automatically intercepted.

A simplification of the known closed cooling cycle can be achieved by supplying the vapour produced in the turbine rotor through a throttle, which is arranged either directly at the vapour outlet from the turbine shaft or in a pipe connected thereto, to the reservoir for the cooling liquid. The reservoir is preferably provided with insertions in which water evaporates while the vapour supplied from the turbine rotor at the primary side condenses. When on the other hand a sufiiciently large vapour network with constant pressure is present besides the gas turbine plant, into which the secondary vapour is fed, it is only necessary to regulate the vapour throttle behind the turbine. In the general case if the vapour production in the rotor increases, the primary side vapour pressure in the reservoir increases somewhat so that a correspondingly larger amount of heat can be transferred to the secondary side.

For the cooling of the cooling liquid present in the reservoir at boiling temperature, a cooler reducing the temperature of the coolant is arranged in the pipe leading from the reservoir to the turbine, in front of the parallel arrangement of check-valve and pump. The heat absorbed by this cooler can be profitably exploited.

he rotor may be constructed as a drum rotor or may consist of discs of equal strength. In order to avoid oscillations at the surface of the cooling liquid in the hollow spaces of the rotor, it is provided with a hollow shaft which passes through the rotor. The interior of the hollow shaft is connected with the hollow spaces in the rotor preferably by radial borings. The vapour pressure in the hollow shaft is regulated by regulating memers at the vapour outlet so that the hollow spaces of the rotor are always completely filled with the cooling liquid. The formation of a free, possibly oscillating, liquid surface is thereby avoided. The number and size of the borings in the hollow shaft are such that the vapour produced in the rotor can be led away without difliculties. Since there is consequently no relaxation space for the coolant evaporated in the rotor, drops of liquid are entrained by the vapour. This is, however, without importance because the separation of vapour and liquid takes place in the reservoir of the coolant outside the rotor. A previous separation of larger drops of liquid can be achieved by providing the internal width of the hollow shaft at its vapour outlet end at a smaller diameter than in its middle part adjacent the interior of the rotor. Within the hollow shaft the large drops of liquid are thrown out by centrifugal force and form a liquid 3 ring which cannot flow out through the smaller internal width. It is true that this liquid ring may perform oscillations. Since, however, these lie on a small diameter, the quiet running of the turbine is not impaired.

The accompanying drawing shows diagrammatically an embodiment of apparatus according to this invention by way of example.

The FIGURE shows the path of the cooling medium passed through a turbine rotor 11. The cooling medium enters through a pipe 2 into the feed-in system of the rotor which in the simplest case consists of a bore 3 in the shaft 4 and two or more radial bores 5 which convey the cooling liquid into the hollow space 6 of the rotor. The hollow shaft 4 has a larger chamber 7 within the rotor. The hollow space 6 of the rotor, which is C0111- pletely filled with cooling liquid, is in communication through bores 8 with the chamber 7 in the shaft 4. In operation, the vapour formed collects in the space 7. Large drops of liquid which have been entrained are separated in the chamber 7 and may possibly form a small liquid ring. The vapour outlet 9 from the shaft has a smaller internal Width than the chamber 7 so that any liquid drops separated from the vapour cannot pass out from the chamber 7. The vapour pressure in the chamber 7 of the rotor shaft can be regulated by a throttle it so that the hollow space 6 of the rotor is filled completely with liquid while the vapour formed fills the chamber 7. Besides the throttle 10, a valve 11 in the vapour pipe 12 may also contribute to this regulation. The pipe 12 connects the vapour outlet point 9 of the rotor shaft with the reservoir 13. In this reservoir, which has a sufficiently large vapour space, the liquid still present in finely divided form in the vapour is completely separated and finally the dry saturated vapour is supplied through a pipe 14 to a vapour network. If the pressure in the vapour network is not constant, the vapour pressure in the reservoir 13 must be regulated by a valve 15. The cooling liquid to be supplied to the rotor 1 is withdrawn from the reservoir through a pipe 16. In the cooler 17 the cooling liquid is cooled down to a temperature considerably below its boiling point. The pump 18 arranged in the circulation of the cooling medium is constructed so that it always conveys a partial amount of the whole of the cooling liquid required. The reduction in amount of cooling medium supplied by the pump 18 should be as small as possible in the situation where the check valve 19 is forced shut. This is best achieved with a piston pump. The remaining partial amount of the cooling medium to be supplied to the rotor in a self conducting manner passes through a check-return valve 19 into the pipe 2 leading to the rotor 1. An amount of cooling liquid equal to that which has been discharged through the conduit 14 in the form of vapour to the network, is introduced into the reservoir 13 through a pipe 20.

We claim:

A method of cooling a turbine rotor by the evaporation of a cooling liquid within said rotor which comprises: passing cooling liquid into a hollow chamber of a rotor, the inner wall of said chamber being defined by a hollow shaft, the hollow space of said shaft and said chamber being connected by a series of borings, conveying part of the cooling liquid to said hollow chamber by means of a constantly operated pump and conveying the remaining portion of said cooling liquid to said rotor by self-conduction through a check valve arranged in a parallel position to said pump, collecting vapor within the hollow space of said shaft, and controlling the rate at which cooling liquid passes into said chamber and vapor exits from said shaft so as to maintain said liquid-containing chamber in a substantially full condition.

References Cited in the file of this patent UNITED STATES PATENTS 2,339,779 Holzwarth I an. 25, 1944 2,369,795 Planiol et al Feb. 20, 1945 2,708,564 Erickson May 17, 1955 2,883,152 Turunen et al Apr. 21, 1959 FOREIGN PATENTS 269,984 Great Britain Apr. 29, 1927 682,295 France Feb. 11, 1930 788,955 France Oct. 5, 1935 818,365 France June 14, 1937 195,736 Switzerland July 16, 1938 910,855 Germany May 6, 1954 OTHER REFERENCES Publication: The Oil Engine The Gas Turbine," March 1958 (pages 434-435). 

